Papers by Keyword: Reaction-Bonded SiC

Abstract: Ceramics based on SiC are characterized by extreme hardness, high thermal conductivity, relatively low thermal expansion and chemical durability. In principle, SiC ceramics can be considered as a long-term stable matrix for final disposal of radioactive waste, such as coated fuel particles (CP) separated from the graphite matrix from spent HTR (high-temperature gas-cooled reactor) fuel pebbles. In the present work, SiC-based ceramic with the embedded UO2 - TRISO (tristructural-isotropic) coated particles was synthesized by the reaction-bonding process. The synthesis was performed in standard SiC crucible. Several physico-mechanical properties of the synthesized samples were investigated. It was shown that the coated particles in the reaction-bonded silicon carbide (RBSiC) matrix are distributed homogeneously. The amount of pores is insignificant and the crippling of the coated particles is not observed. Besides, the junction between CP and RBSiC matrix and between RBSiC matrix and the SiC crucible is very good. For all ceramic components of the synthesized samples, namely, for the UO2-kernels, SiC-layers, SiC crucible wall and for the synthesized RBSiC ceramics, the values of microhardness and fracture toughness were measured and compared with the reference data. The strength properties, such as tensile strength of the synthesized samples, failure mechanism of the reaction-bonded SiC ceramic with embedded UO2 - TRISO coated particles, microstructure of the fracture surfaces, the peculiarities of the coated particles fracture were investigated in detail. Moreover, the diffusion of radioactive tracers (137Cs, 241Am, 36Cl, 3H) across synthesized ceramic was studied and the high safety characteristics of the synthesized ceramic were demonstrated.

Abstract: Silicon carbide is one of the best materials for satellite mirror and chemical vapor deposition (CVD) is an effective method of preparing SiC whiskers and films. In this paper, SiC whiskers or films were deposited on substrates of RB-SiC in an upright chemical vapor deposition furnace of Φ150mm × 450 mm with methyltrichloride silicane (MTS) as precursor gas and H2 as carrier gas under dilute gases of different H2/Ar ratio and different deposition temperature between 1050°C and 1150°C. The morphology and composition of the CVD-SiC grown on RB-SiC substrate were determined by scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. As a result, whisker-like, worm-like or ball-like SiC can be respectively obtained dependent on different deposition conditions such as H2/Ar ratio and deposition temperature, and the composition of the productions are determined as β-SiC by XRD. Furthermore, the deposition mechanisms of different morphologies of SiC are introduced.

Abstract: The oxidation behavior and electrical resistivity of reaction-bonded silicon carbide (RB-SiC) at high temperature (900 °C) had been studied in this paper. The results showed that the weight of RB-SiC would be increased when it was oxidized at 900
. The relationship between the weight-gain of RB-SiC and oxidation times followed the parabolic curve. The oxidation resistance of RB-SiC at 900
could increased by the increase of SiC particles sizes. But the electrical resistivity of RB-SiC had not affected by the oxidation at 900
. The oxidation mechanism of RB-SiC and the affecting factor on oxidation of RB-SiC were analyzed and discussed.

Abstract: The effects of free silicon on thermoelectric properties of reaction-bounded silicon carbide (RB-SiC) were studied. RB-SiC ceramic consists of some free silicon after reaction sintering. Some RB-SiC samples were reheated at high temperature in vacuum to adjust silicon content. The results showed that free silicon affects thermoelectric properties remarkably, especially for the thermoelectric power. A surprising phenomenon was found in SiC/Si composite consisting ~20wt% free-Si, i.e., thermoelectric power, figure of merit Z and ZT are all sharply increased above 400oC. The peak value (4.2X10-4) of ZT appears in original SiC/Si composite at about 500oC, which is increased more than 1000 times than that at room temperature.